tests: k8s: Retry output of kubectl exec in k8s-cpu-ns

We are seeing failures in this test, where the output of
the kubectl exec command seems to be blank, so try
retrying the exec like #11024

Fixes: #11133
Signed-off-by: stevenhorsman <steven@uk.ibm.com>

tests/integration/kubernetes/runtimeclass_workloads/pod-cpu.yaml

@@ -15,7 +15,7 @@ spec:
     image: quay.io/prometheus/busybox:latest
     command:
         - sleep
-        - "30"
+        - "infinity"
     resources:
       limits:
         cpu: "1"